title: Training intensity-dependent and tissue-specific increases in lactate uptake and MCT-1 in heart and muscle.
abstract: We investigated the effects of 3 wk of moderate- (21 m/min, 8% grade) and highintensity treadmill training (31 m/min, 15% grade) on 1) monocarboxylate transporter 1 (MCT-1) content in rat hindlimb muscles and the heart and 2) lactate uptake in isolated soleus (Sol) muscles and perfused hearts. In the moderately trained group MCT-1 was not increased in any of the muscles [Sol, extensor digitorum longus (EDL), and red (RG) and white gastrocnemius (WG)] (P > 0.05). Similarly, lactate uptake in Sol strips was also not increased (P > 0.05). In contrast, in the heart, MCT-1 (+36%, P < 0.05) and lactate uptake (+72%, P < 0.05) were increased with moderate training. In the highly trained group, MCT-1 (+70%, P < 0.05) and lactate uptake (+79%, P < 0.05) were increased in Sol. MCT-1 was also increased in RG (+94%, P < 0.05) but not in WG and EDL (P > 0.05). In the highly trained group, heart MCT-1 (+44%, P < 0.05) and lactate uptake (+173%, P < 0.05) were increased. In conclusion, it has been shown that 1) in both heart and skeletal muscle lactate uptake is increased only when MCT-1 is increased; 2) training-induced increases in MCT-1 occurred at a lower training intensity in the heart than in skeletal muscle; 3) in the heart, lactate uptake was increased much more after high-intensity training than after moderate-intensity training, despite similar increases in heart MCT-1 with these two training intensities; and 4) the increases in MCT-1 occurred independently of any changes in the heart's oxidative capacity (as measured by citrate synthase activity).
authors.affiliation: Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.
authors.forename: S K
authors.initials: SK
authors.lastname: Baker
authors.forename: K J
authors.initials: KJ
authors.lastname: McCullagh
authors.forename: A
authors.initials: A
authors.lastname: Bonen
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001835:Body Weight / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism*; D005260:Female; D066298:In Vitro Techniques; D019344:Lactic Acid / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D027501:Monocarboxylic Acid Transporters; D018482:Muscle, Skeletal / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D010084:Oxidation-Reduction; D010805:Physical Conditioning, Animal / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014018:Tissue Distribution
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D027501:Monocarboxylic Acid Transporters; D019344:Lactic Acid